Technology centered on polymerase chain reaction (PCR) analysisand DNA sequencing has just blown the cover of an anonymouspathogen that masquerades as Lyme disease.

A bacterium by the name of Borrelia Burgdorferi perpetrates Lymedisease, with the connivance of the deer tick, Ixodes scapularis, andits co-conspirators, the deer mouse and the white-tailed deer. Thevery same tick transmits the microorganism, still unnamed, thatcauses human granulocytic ehrlichiosis (HGE). The two infectionshave superficial similarities and significant differences.

For one thing, both have very look-alike symptoms, though Lyme ismilder and less acute than ehrlichia. For another, different antibioticsare often indicated to treat each ailment. And strikingly, the same tickthat bites a victim may inject pathogens from both infectionssimultaneously.

Lyme disease emerged two decades ago in the quaint colonialcommunity of Lyme, Conn. Between 1982 when it became areportable infection, and the end of 1994, the Centers for DiseaseControl and Prevention (CDC), in Atlanta, logged 71,437 cases in 44states. "In 1994 alone," epidemiologist David Dennis of the CDC'soutpost laboratory in Ft. Collins, Colo., told BioWorld Today, "thefigure was 13,043. For 1995, we expect it to top another 10,000."

Human granulocytic ehrlichiosis emerged only in 1992, when adozen patients in Minnesota and Wisconsin hospitals were found toharbor tick-borne pathogens that surprisingly infected a granulocyticwhite blood cell, rather than the monocytes invaded by the well-known Ehrlichia chaffeensis.

That improbable nomenclature refers to Fort Chaffee, Ark., where asoldier was diagnosed in 1991 with ehrlichiosis infecting his bloodmonocytes. Five years earlier, a man traveling in Arkansas acquiredthe same infection from a tick bite.

HGE Bugs' Body Count

"More than 400 cases of human E. chaffeensis infection have beenreported to date, predominantly in the Southeast and mid-Atlanticstates," said infectious disease epidemiologist William Schaffner,"whereas the several dozen reported cases of HGE have occurred inmidwestern and northeastern states."

An article in this week's New England Journal of Medicine (NEJM),dated Jan. 25, 1996, reports the first "Direct cultivation of thecausative agent of human granulocytic ehrlichiosis." Its first author isclinical epidemiologist Jesse Goodman, a specialist in tick-borneinfectious diseases at the University of Minnesota, Minneapolis. "Interms of clearly documented, reported cases," Goodman toldBioWorld Today, "I estimate the total number of HGE cases atbetween 100 and 200, with a mortality rate of around 5 percent _probably less."

He regards these numbers as "very much the tip of the iceberg, sincethe clinical presentation is rather non-specific, and the diagnostictesting non-existent."

Until a diagnostic test comes along, Vanderbilt's Schaffner toldBioWorld Today, "One can start doing large-scale population studiesto define the distribution of this HGE organism in the world.Clinically," he added, "there are pockets of infection with thisorganism. A new one has been discovered in New York state, and theupper reaches of the Mississippi river, in the northern Midwest, hasbeen defined as such a pocket."

He is "reasonably sure that there are other pockets of this infection,as yet undetected. A good serologic test," Schaffner concluded, "willfacilitate detection enormously." Schaffner, chairman of preventivemedicine at Vanderbilt University in Nashville, wrote an editorialaccompanying the NEJM paper.

"The real question is going to be," Goodman observed, "whether weor others can take the material from our infected cell cultures _ nowthat we have grown large numbers of the organisms _ to developimproved antibody assays. That process is just beginning."

To isolate and grow the HGE bacterium, Goodman and his co-authors at the Universities of Maryland and California started with ahuman promyelocytic leukemia cell line, HL60, that "under certainstimuli, can differentiate into cells that behave like true neutrophils[granulocytes] in terms of phagocytosing organisms.

"What we then did," he continued, "was get material from threepatients in whom we highly suspected ehrlichiosis, and from otherpatients as controls."

All three of these index patients, two men and a woman, were in theirsixties. Two came from northern Minnesota, one from northernWisconsin. Both areas are epicenters of ehrlichiosis. All reportedrecent contact with ticks. All had some or all of ehrlichia's hallmarksigns and symptoms: acute onset, high fever, chills, head and muscleaches, nausea and vomiting.

"We found that by PCR we could prove that the patients did indeedhave HGE. In each case we were able to recover the organism fromtheir blood," Goodman said. "And then, within a few days, in thecytoplasm of the cultured cells, we saw development of thepathogenic organisms."

His team did their PCR analysis "with primers that we had designed,specific for this class of organism," he observed.

Besides immunofluorescent testing, Goodman said, "we sequencedthe critical area of the 16S ribosomal DNA gene, where signaturedifferences between this and other ehrlichia microorganisms werepresent."

The three co-authoring universities have jointly applied for a patent"on some of the cultivation techniques described for the agentscausing granulocytic ehrlichiosis," including culture in an embryonictick cell line. The filing's five inventors are all co-authors of theNEJM paper. n

-- David N. Leff Science Editor

(c) 1997 American Health Consultants. All rights reserved.